GB2387979A

GB2387979A - A connector interface for a mobile phone

Info

Publication number: GB2387979A
Application number: GB0209256A
Authority: GB
Inventors: Andrew Wilkes
Original assignee: NEC Technologies UK Ltd
Current assignee: NEC Technologies UK Ltd
Priority date: 2002-04-23
Filing date: 2002-04-23
Publication date: 2003-10-29
Anticipated expiration: 2022-04-23
Also published as: GB0209256D0; GB2387979B

Abstract

A connector interface for a mobile phone permits either a microphone/earpiece headset, or stereo headphones to be connected to the phone using the same three-way jack socket. The microphone bias voltage is used to monitor the impedance between one pair of contacts of the jack socket, when the headset or stereo headphones is connected. The usual electret condenser microphone of a headset has an impedance significantly higher than that of one of the earpiece speakers of stereo headphones. Amplifiers in the interface are then appropriately activated, to amplify the microphone signal if a headset is detected, or supply one of the stereo audio channels if stereo headphones are detected. The common terminal of the jack socket is supplied with a virtual ground potential so that single ended amplifiers can be used to drive the headphones without capacitive coupling.

Description

- 1 - 2387979

A CONNECTOR INTERFACE

Field of the Invention

5 The present invention relates to the field of

connector interfaces, and in particular to the field

of connector interfaces in multimedia appliances which allow for the connection of an external input or output device.

Background to the Invention

The new generation of multimedia portable appliances such as third generation mobile telephones 15 have a dual role of communication and entertainment.

When communicating, two way monophonic sound signals may be passed between the appliance and an external microphone earpiece combination) whereas for listening to music, stereo sound signals may be passed to a pair 20 of stereo headphones. This requires the appliance to be connected either to an external microphone and ear piece combination or to a pair of stereo headphones, depending upon the required role.

However, consumers demand smaller appliances, and 25 so it is becoming increasingly difficult to incorporate both microphone ear piece input/output socket and a separate stereo headphone output socket in the appliances. Therefore, it is advantageous to connect either the microphone ear piece set or the 30 stereo headphones to the appliance using only a single jack plug socket. Conventional solutions in this field use, typically, 5 pole jack connectors. As

these are specialist products and are therefore not "off the shelf", the cost of both the corresponding 35 jack plug socket and the jack plug connector is increased. Additionally, conventional multi media appliances

require coupling capacitors to be placed in the signal lines between the headphones and the stereo amplifiers. This is to remove the direct current component of the output signals from the amplifiers.

5 However, the coupling capacitors reduce the low frequency audio response of the headphones, as well as producing a characteristic 'pop' sound when the headphones are connected and disconnected.

It is an object of the present invention to 10 address these problems.

Statement of Invention

Accordingly the present invention provides a 15 connector interface for connecting an electronic circuit to an external device which can be either a signal source having an output impedance in a first range or a signal user having an input impedance in a second range, said first and second ranges being 20 separated by a predetermined threshold impedance value, the connector interface comprising a connector part having at least a pair of terminals for connection to receive an input signal from or to supply an output signal to the external device, as the 25 case may be; switchable amplifier means switchable between a first mode in which an input signal received on said terminals is amplified for supply to said electronic circuit, and a second mode in which an output signal from the electronic circuit is amplified 30 and supplied to said terminals; and control means operative in response to the impedance applied between said terminal, by an external device connected thereto, to switch said amplifier means to said first mode when said impedance is in said first range and to 35 switch said amplifier to said second mode when said impedance is in said second range.

- 3 In this way, a single jack socket, for example, providing a three-way connection, can be used to connect either a microphone and earpiece headset to the mobile appliance, or a pair of stereo headphones.

5 The interface detects which is being connected and switches the amplifier circuits of the interface accordingly so as either to pass an amplified output corresponding to one stereo audio channel to one earpiece speaker of stereo headphones, or to amplify -

10 and supply to the mobile appliance circuitry the input from the microphone of a headset.

The invention also provides a connector interface for connecting an electronic circuit generating an output signal to an external device for using said 15 output signal, the connector interface comprising a connector part having a first signal terminal and a common terminal for connection to respective terminals; of a corresponding connection part associated with said external device; an output amplifier arranged and 20 connected to supply to said first signal terminal an amplified output signal having a predetermined do component) and a virtual ground line connected to hold said common terminal at the level of said dc component. 25 It is normal practice for the audio outputs of a mobile appliance such as a mobile cellular phone, to employ a single ended amplifier so that the output signal from the amplifier includes a predetermined dc component, usually half the supply voltage for the 30 amplifier. By providing a virtual ground, at this predetermined do potential, to the common terminal of the interface, the amplified audio signals from the mobile unit can be connected directly to the earpiece speakers of the headset or stereo headphones, as the 35 case may be, without the usual decoupling capacitors.

- 4 Brief Description of the Drawings

A specific embodiment will now be described by way of example only and with reference to the 5 following drawings in which: Figure 1A is a schematic view of a headset, including a speaker and microphone, suitable for coupling to a connector interface embodying the present invention; 10 Figure 1B is a schematic view of a pair of stereo headphones suitable for coupling to the connector interface; Figure 2 is a schematic view of a connector interface embodying the present invention and a 15 three-way connector that can be used to connect either the headset of Figure 1A or the pair of stereo headphones of Figure 1B thereto; Figure 3 is a schematic view of a control circuit for controlling the connector interface of Figure 2 20 and Figure 4 is a flow diagram illustrating the operation of the connector interface of Figure 3.

Detailed Description of the Preferred Embodiments

Figure 1A is a schematic view of a headset 20 including an earpiece speaker 18 and a microphone 16, suitable for coupling to a connector interface embodying the present invention. First, second and 30 third headset wires A, B and C provide connections to the microphone 16 and the speaker 18 of the headset as illustrated, wire B being a common connection.

Preferably the microphone 16 is an electret condenser microphone which requires a bias voltage typically 35 between 1 and 20 volts. The electret condenser microphone 16 has an impedance typically ranging from about 1 kOhm to 2 kOhms or more. The impedance of the

- 5 speaker is typically between 8 and 32 Ohms.

Figure 1B shows a schematic view of a pair of stereo headphones suitable for coupling to the connector interface. The headphones 25 comprise left 5 and right earpiece speakers 26 and 28, and similar wires A, B and C to provide connections. Again wire B is common to the two speakers. The speakers 26 and 28 have typical impedances also in the range 8 to 32 Ohms, similar to the speaker of the headset 20 of 10 Figure 1A.

Figure 2 is a schematic view of the connector interface 40 of the present invention together with a three-way jack plug 12 that can be used to connect either the monophonic headset 20 of Figure 1A or the 15 stereo headphones 25 of Figure 1B. The jack plug 12 is of standard design as used for stereo headphone connections to portable hi-fi appliances, and wires A, B and C from the headset 20 or the headphones 25 are connected to the contact points of the plug 20 as 20 illustrated. Thus, the end contact point 38 is connected to wire C, the intermediate contact point 36 is connected to wire B and the contact point 34 nearest the grip part 32 of the plug is connected to wire A. 25 The connector interface 40 incorporates a jack socket to receive the jack plug 12. The jack socket includes contact terminals 60, 62 and 68 for connection with the contact points 34, 36 and 38 respectively of the jack plug 12. Additionally, the 30 jack socket of the interface 42 includes internal contacts 64 and 66. Internal contact 64 makes an electrical connection with the contact 62 of the socket when the jack plug 12 is not inserted, and this connection is broken, providing an open circuit 35 between contact 62 and internal contact 64, when the jack plug is inserted. Similarly, the jack socket includes an internal contact 66 which makes electrical

6 - contact with the contact 68 when the jack plug is not inserted and becomes open circuit when the jack plug is inserted.

Considering now the rest of the interface 40, 5 contact 68 of the jack socket is connected both to an input of a microphone amplifier 48, and an output of an earpiece speaker amplifier 50. Contact 60 is connected to an output of a second earpiece speaker amplifier 56, and contact 62 is connected to the 10 output of a unity gain amplifier 54 providing a predetermined virtual ground potential on the contact 62. Each of amplifiers 48, 50 and 56 is selectively activated by control signals on lines 49, 51 and 53 15 respectively. Contact 68 is also connected to a bias voltage rail 42 via a bias resistor 44. The bias voltage is provided to bias an electret condenser microphone when connected by the jack plug 12 between contact 62 and 20 68.

As mentioned previously, the impedance of a typical electret condenser microphone, such as microphone 16 of headset 20, is 1 kOhm or more, whereas the impedance of a typical earpiece speaker, 25 such as speaker 26 of stereo headphones 25, is 32 Ohms or less. Accordingly, by setting the bias resistor 44 to have a value of say 150 Ohms, the voltage on a signal line 46, connected to the contact 68 of the jack socket, varies between a level close to the bias 30 voltage on rail 42 when an electret condenser microphone is connected between contact 62 and 68, and a value close to the virtual ground potential applied to contact 62, when an earpiece speaker is connected between the contact 62 and 68.

35 A control system, illustrated in Figure 3, monitors the voltage on line 46 when a jack plug 12 is first inserted into the jack socket of the interface,

- 7 and energises amplifiers 48 and 50 by control signals on lines 49 and 51, appropriately, so that the microphone amplifier 48 is activated when the voltage on line 46 is close to the bias voltage on rail 42, 5 and the earpiece speaker amplifier 50 is activated, when the voltage on line 46 is close to the virtual ground potential. When not activated, the amplifiers 48 and 50 present a relatively high input and output impedance respectively.

10 In this way, the interface provides appropriate connections to the contacts of the jack socket, whether the jack plug 12 is connecting to the interface a headset, such as headset 20, or stereo headphones, such as headphones 25.

15 As shown in Figure 2, the interface 40 comprises a further headphone amplifier 56 having an output connected to the contact 60 of the jack socket.

Amplifier 56 provides an amplified signal to the earpiece speaker 18 of headset 20, or earpiece speaker 20 28 of stereo headphones 25. Again the amplifier 56 is activated by a control signal on line 53 as appropriate. -

In accordance with normal practice, earpiece speaker amplifiers 50 and 56 are so called single 25 ended amplifiers, providing an amplified signal including a do component which is typically half the amplifier power supply voltage. Unity gain amplifier 54 is arranged to apply a virtual ground potential to the common contact 62 of the jack socket which is 30 substantially equal to the level of the do component of the output signals from amplifiers 50 and 56. In this way, the amplifiers 50 and 56 can be connected to the earpiece speakers 26 and 28 of stereo headphones 25 without the usual series connected decoupling 35 capacitors. The reduction in low frequency response caused by such a series coupling capacitor is thereby avoided. Furthermore, if the virtual ground potential

- 8 applied to contact 62 is closely matched to the dc component of the output signals of amplifiers 50 and 56, the jack plug 12 can be inserted and removed from the jack socket of the interface without the usual 5 popping noise in the earpiece speakers of the stereo headphones 25. Similar improvements in low frequency performance and reduction in connection noise is achieved for the single earpiece speaker 18 of the headset 20.

10 The internal contact 64 associated with contact 62 of the jack socket of the interface is connected to ground via a resistor 60. When no jack plug is inserted in the jack socket of the interface, the internal contact 64 is connected to contact 62 and is 15 thus held at the virtual ground potential generated by unity gain amplifier 54. However, when a plug 12 is inserted in the jack socket, the connection between internal contact 64 and contact 62 is broken, so that resistor 60 pulls the voltage on internal contact 64 20 down to ground. A line 58 connected to the internal contact 64 provides a control signal indicating whether a jack plug 12 has been inserted into the jack socket. This is useful in allowing the interface to detect whether an external device such as a headset or 25 stereo headphones has been connected to the interface and energising the interface amplifiers only if a jack plug is present. This is important for power saving.

Referring now to Figure 3, this illustrates the interconnection of the interface 40 illustrated in 30 Figure 2 with its control logic. Parts common to the circuit of Figure 2 are given the same reference numerals. In Figure 3, the resistor 81 corresponds to the impedance of the electret condenser microphone or the earpiece speaker which may be connected between 35 contacts 62 and 68 of the jack socket of the interface. The resulting voltage on line 46 is compared by a comparator 78 with a fixed potential

- 9 determined by a potential divider formed by resistors 76 and 77 connected between the voltage bias rail 42 and the virtual ground potential from the unity gain amplifier 54. Typically, resistors 76 and 77 may have 5 the same value so that the reference voltage applied to the inverting input of comparator 78 is halfway between the bias voltage and the virtual ground.

Accordingly, the output of comparator 78 is high if the value of resistor 81 is greater than resistor 44, 10 indicating that an electret condenser microphone has been connected, and is low if resistor 81 is lower than resistor 44, indicating that an earpiece speaker of stereo headphones have been connected. The output of comparator 78 is supplied to control logic 80 which 15 provides control signals on lines 49 and 51 to activate one of amplifiers 48 and 50 accordingly.

Resistors 75 and 79 are connected in series between the voltage bias rail 42 and ground (zero volts), forming a potential divider controlling the 20 non-inverting input of the unity gain amplifier 54.

If the power supply to amplifiers 50 and 56 is derived from the voltage bias rail 42 and ground, so that the do component of the output signals of amplifiers 50 and 56 is approximately half of the bias voltage on 25 rail 42, then resistors 75 and 79 may be of equal value so that the virtual ground potential derived from the output of unity gain amplifier 54 is also at half the bias voltage.

The connection between the internal contact 64 30 and contact 62 of the jack socket, as illustrated in Figure 2, is shown in Figure 3 as switch 82.

Accordingly, when the signal on line 58 supplied to control logic 80 is high, at the virtual ground potential, this indicates that there is no jack plug 35 inserted in the jack socket of the interface and so control logic 80 deactivates all the amplifiers 48, 50 and 56 by appropriate control signals on lines 49, 51

- 10 and 53. When the signal on line 58 drops to zero volts, this indicates that a plug has been inserted and control logic 80 then activates amplifiers in accordance with the status of the signal on the line 5 from the output of comparator 78.

A further function of the control logic 80 which is not specifically illustrated in Figure 3 may be to remove the bias voltage specifically from contact 68 of the jack socket, when the control logic 80 has 10 identified that stereo headphones have been connected.

For this purpose, an additional switch operated by the control logic 80 can be included in series with the resistor 44. Further, the control logic 80 may be effective to apply the bias to contact 68, only once 15 the presence of a plug inserted into the jack socket of the interface has been detected.

Figure 4 is a state diagram illustrating the operation of the control system and is self explanatory. 20 The interface has been illustrated in Figure 2 with separate microphone and earpiece speaker amplifiers 48 and 50 which are selectively, and mutually exclusively, activated in accordance with the detected voltage on line 46. It is also possible to 25 use a single amplifier with suitable input and output switching controlled by control logic 80. The single amplifier may have its input connected to contact 68 and its output supplying an amplified signal to the internal circuits of the mobile appliance, when a 30 microphone is detected, and may be switched to have its output connected to contact 68 and its input supplied with a signal from the internal circuits of the mobile appliance, when a stereo headphone is detected.

Claims

- 11 CLAIMS:

1. A connector interface for connecting an electronic circuit to an external device which can be 5 either a signal source having an output impedance in a first range or a signal user having an input impedance in a second range, said first and second ranges being separated by a predetermined threshold impedance value, the connector interface comprising: 10 a connector part having at least a pair of terminals for connection to receive an input signal from or to supply an output signal to the external device, as the case may be; switchable amplifier means switchable between a 15 first mode in which an input signal received on said terminals is amplified for supply to said electronic circuit, and a second mode in which an output signal from the electronic circuit is amplified and supplied to said terminals) and 20 control means operative in response to the impedance applied between said terminal, by an external device connected thereto, to switch said amplifier means to said first mode when said impedance is in said first range and to switch said amplifier to 25 said second mode when said impedance is in said second range. 2. A connector interface as claimed in claim 1, including an electrical bias source connectable across 30 said pair of terminals, said control means being arranged to respond to the voltage across said pair of terminals on connection of an external device thereto.

3. A connector interface as claimed in claim 2, 35 wherein said control means is further operative to remove said electrical bias from said pair of terminals when said amplifier means is switched to

said second mode.

4. A connector interface as claimed in any preceding claim, wherein said pair of terminals comprise a first 5 signal terminal and a common terminal, and said amplifier means, when is said second mode, supplies to said first signal terminal an amplified output signal having a predetermined do component, the interface further comprising 10 a virtual ground line connected to hold the common terminal at the level of said do component.

5. A connector interface as claimed in any preceding claim, wherein said connector part is one part of a 15 plug and socket connector and it includes at least one pair of switch contacts operated on mating of the parts of said plug and socket connector, and the interface further includes a sense circuit responsive to operation of said switch contacts to energise said 20 amplifier means only when said connector part is mated with a corresponding connector part.

6. A connecter interface as claimed in claim 5, as dependent on claim 4, wherein one of said pair of 25 switch contacts is connected to said common terminal.

7. A connector interface for connecting an electronic circuit generating an output signal to an external device for using said output signal, the 30 connector interface comprising a connector part having a first signal terminal and a common terminal for connection to respective terminals of a corresponding connector part associated with said external device; an output amplifier arranged and connected to 35 supply to said first signal terminal an amplified output signal having a predetermined do component; and a virtual ground line connected to hold said

- 13 common terminal at the level of said do component.

8. A mobile telecommunications handset comprising: a transmitter for transmitting data to a base = 5 station; a receiver for receiving data from a base station; and a connector interface as claimed in any preceding claim. -

10 - 9. A multi media appliance comprising: a generating means for generating a signal to be output from the appliance;.

a receiving means for receiving a signal to be -

15 input to the appliance; and a connector interface as claimed in any of claims 1-7. 10. A method for connecting an electronic circuit to 20 an external device which can be either a signal source having an output impedance in a first range or a signal user having an input impedance in the second range, said first and second ranges being separated by a predetermined threshold impedance value, the method 25 comprising the steps of: -

receiving an input signal from or supplying an output signal to the external device, as the case may be; and switching a switchable amplifier means between a 30 first mode in which an input signal received from the external device is amplified and supplied to the electronic circuit, and a second mode in which an output signal from the electronic circuit is amplified and supplied to the external device, wherein said -

35 switchable amplifier means is switched to said first mode when the impedance is in the first range and -

switched to said second mode when said impedance is in

the second range.

11. A method for connecting as claimed in claim 10, further comprising the steps of: 5 connecting an electrical bias across said pair of terminals) and switching the switchable amplifier means to either said first or second mode in response to the voltage across said pair of terminals on connection of 10 an external device thereto.

12. A method for connecting as claimed in claim 11, further comprising the step of: removing said electrical bias from said pair of 15 terminals when the amplifier means is switched to said second mode.

13. A method for connecting as claimed in any of claims 10-12, further comprising the steps of: 20 supplying an amplified output signal having a predetermined do component to a first signal terminal, when said amplifier means is in said second mode; and holding a common terminal at the level of said dc component. 14. A method of connecting as claimed in any of claims 10-13, further comprising the steps of: operating, on the connection of said external device, at least one pair of switch contacts; and 30 energizing said amplifier means, in response to said operation of said switch contacts, only upon connection of said external device.

15. A method of connecting as claimed in claim 14, as 35 dependent upon claim 13, further comprising the step of: connecting one of said pair of switch contacts to

- 15 said common terminal.

16. A method for connecting an electronic circuit generating an output signal to an external device for 5 using said output signal, the electronic circuit comprising a connector part having a first signal terminal and a common terminal for connection to respective terminals of a corresponding connection part associated with the external device, the method 10 comprising the steps of: supplying to said first signal terminal an amplified output signal having a predetermined dc component; and holding said common terminal at the level of said 15 dc component.

17. A connector interface substantially as herein described with reference to the accompanying drawings.

20 18. A method of connecting an electronic circuit to an external device substantially as herein described with reference to the accompanying drawings.